For the past 6 months I've been having the p0505 issue where the car would jerk/bounce rpms around 1700 and idle high/hunting. After posting to many sites and troubleshooting, and checking for vac leaks, replacing iacv, adjusting idle etc with nothing working, I finally found the issue. CHECK YOUR AIR ASSIST SOLENOID! If I
Am correct it is designed to allow more air into the engine when cold to help allow the car to reach temp, and when the car reaches roughly 150 degrees it's suppose to shut itself. After testing, mine was staying open all the time! I hope this may be of some help, if you've checked everything else dont forget to check this! My car has been like new ever since. Car is a 1999 civic ex manual.

 

You simply found the solution to your specific problem. Nice figuring it out though! Must have been frustrating with crappy idle lol.

 

For sure, just want to give people a heads up of another possible thing causing the annoying problem lol

 

 

Worth mentioning, I believe this solution will only work for 99-00 Civics. I don't think that 92-97 have the AAV.

 

Only 99-00 Y8s